SU‐GG‐T‐323: Angular Distribution of Neutron Fluence and Its Effect On Shielding for a Passively‐Scattered Proton Therapy Unit
SU‐GG‐T‐323: Angular Distribution of Neutron Fluence and Its Effect On Shielding for a Passively‐Scattered Proton Therapy Unit
复制标题
SU-GG-T-323：中子注量的角分布及其对被动散射质子治疗装置屏蔽的影响
DOI：
10.1118/1.2962075
复制
发表时间：
2008
期刊：
影响因子：
3.8
通讯作者：
D. Low
中科院分区：
文献类型：
--
作者：
Y. Zheng;W. Newhauser;E. Klein;D. Low
目的：中子产生是质子治疗装置屏蔽的主要问题。传统上，中子计算是基于分析方法，不考虑实际的束流成形组件和喷嘴屏蔽。本研究的目的是计算中子能谱注量产生的被动散射质子治疗单元与详细的蒙特卡罗建模，并估计相应的中子剂量当量和屏蔽要求，在不同的角度相对于束流方向。方法和材料：利用MCNPX对被动散射质子治疗机的距离调制器、散射器、距离转换器和孔径等关键部件进行了建模。模拟了不同角度和不同距离下的中子注量率谱。然后使用国际辐射防护委员会（ICRP）出版物74中的转换因子将中子谱注量转换为中子剂量当量。根据中子剂量当量和能谱注量，对朝向束流和平行于束流的壁的屏蔽要求进行了评估。结果：中子能谱注量随与束流的夹角变化显著。高能中子的前向峰值随入射角的增大而减小。低能中子随角度变化不大。治疗室内的中子剂量当量随角度变化不明显，但由于高能中子在零度时最大，因此朝向射束的墙壁比其他墙壁需要更多的屏蔽。结论：质子治疗机的中子能谱注量随与束流方向的夹角变化而显著变化。与解析方法相比，蒙特卡罗模拟结果为屏蔽设计提供了更准确的中子角分布估计。
Purpose:Neutron production is of principal concern in shielding of proton therapy units. Conventionally, neutron calculations are based on the analytical methods, which do not take the actual beam shaping components and the nozzle shielding into account. The goal of this study was to calculate neutron spectral fluence produced at a passive scatteringproton treatment unit with detailed Monte Carlo modeling and to estimate the corresponding neutrondose equivalent and shielding requirements at various angles relative to the beam direction. Method and Materials: We modeled all key components in the nozzle including a range modulator,scatter, range shifter and aperture for a passive scatteringproton therapy unit with MCNPX. We simulated the spectral neutron fluences at different angles and distances around the nozzle. The neutron spectral fluences were then converted to neutrondose equivalent using conversion factors from International Committee of Radiological Protection (ICRP) Publication 74. Based on the neutrondose equivalent and spectral fluence, the shielding requirements for walls facing the beam and parallel to the beam were assessed. Results: The spectral neutron fluence varied significantly with angle relative to the beam. High energy neutrons were forward peaked and decreased with increasing angle. Low energy neutrons did not change much with angle. Neutrondose equivalent in treatment room did not change significantly with angle, but more shielding was required for the wall facing the beam than other walls because the high energy neutrons were greatest at zero degrees. Conclusion: The neutron spectral fluence from proton therapy units changes significantly with angle relative to the beam direction. Compared to the analytical methods, Monte Carlo simulated results provided a more accurate estimation of the neutronangular distribution for shielding design.